1. Field of the Invention
This invention relates to an apparatus for automatically feeding sheets to an image forming device such as a copying machine, and more particularly to an automatic sheet feeding apparatus equipped rationally with a register means for properly correcting the orientation of a feeding sheet with relation to a feeding direction.
2. Description of the Prior Art
There has been used an automatic sheet feeding apparatus such as a document feeder in an image forming device such as a copying machine, facsimile and image scanner, in which one or more original documents stacked on a document supply tray are automatically fed one by one to an image reading portion of the image forming device, and the original document after subjected to image reading at the image reading portion is automatically sent out to a discharge tray. The document feeding device is generally provided on the route from the document supply tray to the image reading portion with a register means for properly correcting the orientation of the document being forwarded with relation to a feeding direction. With the register means, even if the original document is forwarded at a slant relative to the document feeding direction (longitudinal direction of a document feeding passage), the document advancing obliquely (with its leading edge thereof being not orthogonal to the document feeding direction) is corrected in its posture to the proper feeding direction (as a result, the leading edge of the document becomes orthogonal to the document feeding direction).
The register means as noted above has functions of not only making the posture of the document to be fed proper, but also determining timing of reading the image on the document at the image reading portion.
Describing now in detail the document registering function of the register means for properly feeding the original document with reference to FIG. 1A and FIG. 1B, there is shown the register means R of the automatic document feeding device applied to the image forming device such as a copying machine and facsimile, which usually comprises a pair of rollers r1 and r2 which come in contact with each other on a document feeding passage W. The rollers r1 and r2 rotate in opposite directions so as to forward the document along the document feeding passage W in the feeding direction (arrow a).
Until the document advancing along the feeding passage arrives at a contact line (nip point Np) of the rollers r1 and r2, the rollers r1 and r2 are not yet rotated. Then, the rollers r1 and r2 are started to rotate immediately after the document collides with the rollers at the nip point.
That is, in the case where the document D advancing along the feeding passage W is slanting with relation to the feeding direction unlike a properly oriented document Da as illustrated in FIG. 1A, the document D is forwarded until colliding with the nip point Np of the rollers and moved some more forwardly after it collides with the nip point Np, with the consequence that the document D is slightly bent at its leading portion as shown in FIG. 1B.
Consequently, the leading edge of the slanting document D thus bent slightly comes into linear contact with the nip point Np and is aligned orthogonally to the forwarding direction. Thereafter, the rollers r1 and r2 are started to rotate to forward the document, so that the document passing through the rollers assumes its posture oriented to the proper feeding direction as indicated by the imaginary line Dx in FIG. 1B. Thus, correction of the orientation of the document being forwarded toward the image reading portion is accomplished.
In the illustrated register means R, one of the rollers r1 and r2 may be driven, and the other roller may come in frictional contact with the driving roller.
A conventional automatic document feeding device incorporating the register means of this type is schematically shown in FIG. 2A as one example, which is applicable to a digital copying machine or a facsimile. In general, such a document feeding device as illustrated is placed on the image forming device M such as a copying machine and comprises a document supply tray 1 for stacking one or more original documents to be subjected to image reading, a document delivery means including a kick roller 3a for sending out the documents one by one from the document supply tray 1 into a feeding passage W, a large-diameter feed roller 5 for forwarding the document from the document supply tray toward an image reading point Px, and a register roller 7 coming in press contact with the feed roller 5. While the document passes through the image reading point Px defined beneath the feed roller 5, the image on the document is read with an image reading element IR such as an image sensor mounted in the image forming device M.
The register roller 7 in this document feeding device corresponds to the roller r1 in the device shown in FIG. 1, and the large-diameter feed roller 5 corresponds to the roller r2 in FIG. 1. So, the rollers 5 and 7 constitute a register means R.
Accordingly, until the document D sent from the document supply tray 1 into the feeding passage W comes into collision with the nip point Np of the feed roller 5 and the register roller 7, the rollers 5 and 7 are kept from rotating. Thereafter, when the document D collides with the nip point Np, and then, is slightly bent as shown in FIG. 2A, the rollers 5 and 7 resting at this point are started to rotate. That is, even if the document is sent from the document supplying tray 1 at the slant with relation to the document feeding direction, the leading edge of the slanting document is aligned with the nip point Np of the rollers 5 and 7, which is orthogonal to the document feeding direction. The rollers 5 and 7 are started to rotate in such a state that the leading edge of the document comes in straight contact with the contact line between the rollers, consequently to cause the document to be oriented straight to the proper forwarding direction and properly forwarded along the feeding passage W. In a case where a plurality of documents are handled, the large-diameter feed roller must be repeatedly stopped and started to rotate.
Conventional sheet feeding apparatuses similar or equivalent in mechanism to the aforesaid structure are disclosed in Japanese Patent Application Public Disclosures Nos. SHO 52-53430(A) (corresp. to U.S. application. Ser. No. 624,860 filed Oct. 23, 1975), SHO 57-1780(A), SHO 58-31837(A), and HEI 7-199556(A).
These sheet feeding apparatuses have a tendency to increasing the inertial mass of the feed roller 5 so as to move the document or sheet stably and smoothly. Furthermore, in order to secure a circulating passage around the feed roller 5, through which the document passes to be automatically turned over for the purpose of reading images on both sides of the document, the circumference of the feed roller 5 should be made longer than the length of the document to be handled. Thus, the feed roller 5 should be made large in diameter, with the consequence that the large-diameter feed roller, which must be repeatedly stopped and started to rotate for correcting the orientation of the document being forwarded, necessitates large starting torque when being started to rotate.
Accordingly, each time the original document fed to the aforementioned document feeding device is connected in its orientation, the large-diameter feed roller 5 is highly wasteful energy for repeatedly starting and stopping. Besides, the feed roller having relatively large mass inevitably entails a disadvantage such that it becomes dull in starting the rotation, thereby to cause delay of movement, and impedes smooth and continuous operation for feeding the document, and that the automatic sheet feeding apparatus incorporating the large-mass feed roller cannot be operated at high speed.